Coating composition

ABSTRACT

This invention relates to a liquid coating composition that is thermally-curable in the presence of oxygen, comprising: a monomer or oligomer containing two or more acrylate and/or methacrylate functional groups; an azo initiator; and oxygen. This invention also relates to a process for coating a substrate comprising the steps of applying a thin film of the foregoing coating composition to said substrate; and heating said coating composition at an effective temperature for an effective period of time to cure said coating composition, said applying and heating steps being conducted in the presence of oxygen.

This application claims the benefit of U.S. Provisional Application No.60/063984, filed Nov. 6, 1997.

TECHNICAL FIELD

This invention relates to coating compositions. More particularly, thisinvention relates to liquid coating compositions that are thermallycurable in the presence of oxygen and are comprised of a multifunctional(meth)acrylate monomer or oligomer, an azo initiator and oxygen.

BACKGROUND OF THE INVENTION

The coatings industry is constantly searching for new technologies thatto will reduce or eliminate the amount of volatile organic compounds(VOCs) in industrial paints and coatings. High solids solvent bornecoatings, water based coatings, powder coatings and radiation cured(ultraviolet and electron beam) coatings are technologies thatsignificantly reduce the amount of VOCs relative to traditional solventborne coatings. Each of the aforementioned technologies has limitations.Thermally cured solvent borne coatings still dominate the industrybecause suitable substitutes for many coatings have not been found.

With the exception of ultraviolet and electron beam cured coatings andcoatings comprising polyallyl glycidyl ethers, (meth)acrylate functionalresins and coatings are not used in industrial coating applications. Aprimary reason for this is that atmospheric oxygen inhibits the curingprocess. Oxygen inhibited coatings cure at a low rate, often remaintacky, and exhibit poor tensile strength and durability, resulting infilm properties that are unsuitable for industrial paints and coatings.

Ultraviolet curing of acrylate films in air is practical because thehigh density of initiating radicals generated during irradiationconsumes dissolved oxygen faster than oxygen can diffuse back into thefilm. During irradiation, polymerization proceeds in a quasi-anaerobicenvironment.

Attempts to derive the benefits of free radical chemistry by thermallycuring thin, high solids acrylate coatings similar to those used inultraviolet and 30 electron beam cured coatings have producedunder-cured films with marginal solvent resistance. This is true evenunder practical anaerobic conditions. In practice, the total exclusionof oxygen is difficult in commercial coating operations.

Polyallyl glycidyl ether resins have been used in two-component,high-solids, thermally cured coatings that comprise (meth)acrylatemonomers and oligomers. These coatings are two component systems withlimited pot life and are expensive due to the high cost of the polyallylglycidyl ether component. Additionally, they require oxygen and driercompounds such as cobalt carboxylates, and require solvent for sprayapplication. Polyallyl glycidyl ether resins have been commerciallyavailable since the early 1990's, but have only achieved very limiteduse in industrial paints and coatings due to their limitations.

The present invention provides a replacement for many traditionalthermally cured solvent borne coatings. In one embodiment of thisinvention, a solventless coating is provided that can be applied viatraditional/existing spray application equipment, and cured intraditional existing cure ovens at traditional cure temperatures andbake times. This embodiment can be characterized as a one-component,storage-stable, solventless, thermally curable, (meth)acrylatefunctional, clear or highly pigmented paint or coating with a VOCcontent lower than solvent or water borne coatings and equal to or lessthan powder coatings. These (meth)acrylate functional coatings can becured in the presence of atmospheric oxygen. This embodiment is costcompetitive with traditional general industrial coatings and is expectedto result in a significant reduction in VOC emmisions introduced intothe atmosphere.

SUMMARY OF THE INVENTION

This invention relates to a liquid coating composition that isthermally-curable in the presence of oxygen, comprising: a monomer oroligomer containing two or more acrylate and/or methacrylate functionalgroups; an azo initiator; and oxygen. This invention also relates to aprocess for coating a substrate comprising the steps of applying a thinfilm of the foregoing coating composition to said substrate; and heatingsaid coating composition at an effective temperature for an effectiveperiod of time to cure said coating composition, said applying andheating steps being conducted in the presence of oxygen.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The monomers or oligomers containing two or more acrylate and/ormethacrylate functional groups that are useful with this invention canbe any such monomers or oligomers known in the art. These are sometimesreferred to as multifunctional (meth)acrylate monomers or oligomers.These multifunctional (meth)acrylate monomers or oligomers includedifunctional, trifunctional, tetrafunctional, pentafunctional andhexafunctional monomers and oligomers. The difunctional andtrifunctional monomers and oligomers are especially useful. Thesemonomers and oligomers may include other functional groups other thanthe acrylate and/or methacrylate functional groups. These otherfunctional groups include epoxy, hydroxyl, carboxyl, sulfonic,phosphonic, isocyanate, vinyl, allyl, halide (e.g., fluoride, iodide,bromide), amine, sulfonamide, carbamide, carbodiimide, cyano,acetylenic, aldehyde, peroxy, hydroperoxy, azo, peroxyester, andcombinations of two or more of the foregoing. The monomers and oligomersthat are useful typically have molecular weights in the range of about200 to about 5000, and in one embodiment about 200 to about 3000, and inone embodiment about 300 to about 1000.

In one embodiment, the multifunctional (meth)acrylate monomer oroligomer is a compound represented by the formula ##STR1## wherein informula (I): R is a hydrocarbon group, a siloxane group, a partiallyfluorinated hydrocarbon group or a perfluorocarbon group;

each A is independently a divalent group derived from an epoxide, amixture of diol and dicarboxylic acid, a lactone, a lactam, an aminoacid, a hydroxy acid or lactide;

each B is independently hydrogen, a hydrocarbon group, a siloxane group,a partially fluorinated hydrocarbon group or a perfluorocarbon group, ora group represented by the formula ##STR2## wherein in formula (II) R¹is hydrogen, a hydrocarbon group, a siloxane group, a partiallyfluorinated hydrocarbon group, or a perfluorocarbon group;

x is a number in the range from zero to about 50, and in one embodimentabout zero to about 15; and

y is a number in the range from 2 to about 10, and in one embodiment 2to about 6.

R in formula (I) a hydrocarbon group, a siloxane group, a partiallyfluorinated hydrocarbon group or a perfluorocarbon group containing upto about 50 carbon atoms, and in one embodiment about 5 to about 20carbon atoms. R can be a straight chain or branched chain hydrocarbongroup. The group R may also contain one or more oxygen, nitrogen, sulfurand/or halide atoms (e.g., fluoride, bromide, iodide). The group R cancontain one or more hydroxyl, carboxyl and/or amine groups.

The group A in formula (I) contains 1 to about 25 carbon atoms, and inone embodiment about 2 to about 12 carbon atoms. The epoxides which A isderived from include ethylene oxide, propylene oxide, glycidylmethacrylate, and the like. The diols from which A is derived includeethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol, dipropylene glycol, neopentyl glycol, 1,2-, 1,3- and1,4-butanediols, hexane diol, caprolactone diol, caprolactone triol, andthe like. The dicarboxylic acids include succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, and the like. Thelactones include propiolactone, butyrolactone, valerolactone,caprolactone, and the like. The lactams include propiolactam,butyrolactam, valerolactam, caprolactam, and the like. The amino acidsinclude 3-amino propionic acid, 4-amino butyric acid, 5-amino valericacid, 6-amino caproic acid, 7-amino heptanoic acid, 8-amino octanicacid, and the like. The hydroxy acids include lactic acid, 4-hydroxybutyric acid, 5-hydroxy valeric acid, 6-hydroxy caproic acid, 7-hydroxyheptanoic acid, 8-hydroxy octanoic acid, and the like. Mixtures of theforegoing may be used.

The hydrocarbon groups B independently are straight chain or branchedchain groups of 1 to about 50 carbon atoms, and in one embodiment about1 to about 1 6 carbon atoms.

The partially fluorinated or perfluorocarbon groups B independently arestraight chain, branched chain or cyclic groups. These groups typicallycontain 1 to about 50 carbon atoms, and in one embodiment about 1 toabout 16 carbon atoms. These partially fluorinated or perfluorocarbongroups typically contain about 3 to about 33 fluorine atoms, and in oneembodiment about 3 to about 15 fluorine atoms.

The group R¹ in formula (II) can be hydrogen, a hydrocarbon group, asiloxane group, a partially fluorinated hydrocarbon group or aperfluorocarbon group of up to about 20 carbon atoms, and in oneembodiment about 1 or about 2 carbon atoms. R¹ can be a partiallyfluorinated or perfluorocarbon hydrocarbon group which can be a straightchain or branched chain group containing 1 to about 20 carbon atoms, andin one embodiment about 2 to about 8 carbon atoms, and about 3 to about33 fluorine atoms, and in one embodiment about 3 to about 15 fluorineatoms.

Examples of the difunctional monomers and oligomers that are usefulinclude triethylene glycol dimethacrylate, ethylene glycol diacrylate,ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate,polyethylene glycol dimethacrylate, 1,3 butylene glycol diacrylate,1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, diethyleneglycol diacrylate, diethylene glycol dimethacrylate, 1,6 hexanedioldiacrylate, 1,6 hexanediol dimethacrylate, neopentyl glycol diacrylate,neopentyl glycol dimethacrylate, tetraethylene glycol diacrylate,triethylene glycol diacrylate, 1,3 butylene glycol dimethacrylate,tripropylene glycol diacrylate, tripropylene glycol dimethacrylate,polyethylene glycol diacrylate, cyclohexane dimethanol dimethacrylate,cyclohexane dimethanol diacrylate, ethoxylated bisphenol A diacrylate,ethoxylated bisphenol A dimethacrylate, propoxylated neopentyl glycoldiacrylate, propoxylated neopentyl glycol dimethacrylate, alkoxylatedaliphatic diacrylates, alkoxylated aliphatic dimethacrylates, and thelike.

Examples of the trifunctional monomers and oligomers that are usefulinclude trimethylolpropane trimethacrylate, trimethylolpropanetriacylate, tris (2-hydroxy ethyl) isocyanurate triacrylate, ethoxylatedtrimethylolpropane triacrylate, pentaerythritol triacylate, propoxylatedtrimethylolpropane triacrylate, propoxylate trimethylolpropanetrimethacrylate, propoxylated glyceryl triacrylate, tris (2-hydroxyethyl) isocyanurate trimethacrylate, ethoxylated trimethylolpropanetrimethacrylate, pentaerythritol trimethacrylate, propoxylated glyceryltrimethacrylate, and the like. Propoxylated trimethylolpropanetri(meth)acrylate is especially useful.

Examples of the tetrafunctional, pentafunctional and hexafunctionalmonomers and oligomers that are useful include pentaerythritoltetraacrylate, di-trimethylolopropane tetraacrylate, dipentaerythritolpentaacrylate, ethoxylated pentaerythritol tetraacrylate, pentaacrylateester, pentaerythritol hexaacrylate, pentaerythritol tetramethacrylate,ditrimethylolopropane tetramethacrylate, dipentaerythritolpentamethacrylate, ethoxylated pentaerythritol teteramethacrylate,pentaerythritol hexamethacrylate, and the like.

Mixtures of two of more of any of the foregoing multifunctional(meth)acrylate monomers or oligomers can also be used.

Examples of commercially available multifunctional (meth)acrylatemonomers and oligomers that can be used include SR 492 (a product ofSartomer Company under the trade designation SR 492 (propoxylated₃trimethylol propane triacrylate) and SR-501 (propoxylated₆ trimethylolpropane triacrylate). The term "propoxylated₃ "refers to the fact thatthere are three propoxy groups, i.e., (C₃ H₆ O)₃, in SR 492. Similarly,the term "propoxylated₆ " refers to the fact that there are six propoxygroups, i.e., (C₃ H₆ O)₆, in SR-501. Thus, SR 492 may be represented bythe formula ##STR3## Similarly, SR 501 may be represented by the formula##STR4##

In one embodiment, the multifunctional (meth)acrylate monomer oroligomer is a urethane-containing multifunctional (meth)acrylate monomeror oligomer. These can be prepared by reacting a hydroxy-containingmonofunctional (meth)acrylate monomer or oligomer with a multifunctionalisocyante, optionally in the presence of a catalyst. Thehydroxy-containing monofunctional (meth)acrylate monomers or oligomersthat can be used include those represented by the formula ##STR5##wherein in formula (III): R is hydrogen or methyl; R¹ is a hydrocarbongroup of 1 to about 12 carbon atoms, and in one embodiment about 2 orabout 3 carbon atoms; each A is independently a divalent group derivedfrom an epoxide, a mixture of diol and dicarboxylic acid, a lactone, alactam, an amino acid, a hydroxy acid or lactide; and y is a number inthe range of zero to about 20. The divalent groups A can be derived fromthe same compounds discussed above with respect to formula (I). Examplesof the hydroxy-containing monofunctional (meth)acrylate monomers oroligomers that can be used include hydroxy propyl acrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, hydroxy ethyl methacrylate,caprolated hydroxy ethyl (meth) acrylate, caprolated hydroy propyl(meth) acrylate, and the like. The isocyantes that can be used includepolymeric isocyanates, modified isocyanates, isocyanate prepolymers,biurets, uretidiones and isocyanurates. Examples of useful isocyanatesinclude isophorone diisocyante, hexamethylene diisocyanate,4,4'-methylene bis(cyclohexyl isocyanate), bis(4-isocyanatocyclohexyl)methane, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,4,4'-diphenylmethane diisocyanate, tetramethyl-1,3-xylene diisocyanate,and the like. The equivalent ratio of hydroxy funtional (meth)acrylatemonomer or oligomer to isocyanate is generally from about 0.1 to about1.1 and in one embodiment about 0.98 to about 1.02. The catalysts thatcan be used include organo tin catalysts, such as dibutyl tin dilaurate,stannous octoate, and like, as well as potassium octoate. Commerciallyavaiable catalysts from Air Products under the tradenames Metacure andPolycat 46 can be used. These include Metacure K-15 (potassium octoate),Metacure T-95, T-96, T-10, T-16 (stannous octoate), and Metacure T-12(dibutyl tin dilaurate). The amount of catalyst that is used istypically up to about 0.5% by weight based on the weight of the acrylatemonomer or oligomer and the isocyante, and in one embodiment about 0.001to about 0.1% by weight, and in one embodiment about 0.005 to about0.05% by weight. The reaction temperature is generally from about 20° C.to about 120° C. These monomers or oligomers typically have molecularweights in the range of about 300 to about 2500, and in one embodimentabout 300 to about 700.

Mixtures of the foregoing multifunctional meth(acrylate) monomers oroligomers and the foregoing urethane-containing multifuctional(meth)acrylate monomers or oligomers can be used.

In one embodiment, the inventive coating composition is characterized bythe absence of fluorine-containing acrylate or methacrylate monomers oroligomers.

The inventive coating compositions typically contain from about 5% toabout 99.9% percent by weight of the multifunctional (meth)acrylatemonomer or oligomer, and in one embodiment from about 90% to about 99%by weight of such monomer or oligomer for clear coatings, and in oneembodiment about 25% to about 90% by weight of such monomer or oligomerfor pigmented coatings.

The azo initiator can be any azo compound known in the art forinitiation of (meth)acrylate polymerizations. These include2,2'-azobis(2,4-dimethylpentanenitrile),2,2'-azobis(2-methylpropanenitrile), 2-2'-azobis(2-methylbutanenitrile),and 1,1'-azobis (cyclohexanecarbonitrile). The foregoing azo compoundsare commercially available from DuPont under the trade designations Vazo52, Vazo 64, Vazo 67 and Vazo 88, respectively. Additional azo compoundsthat are useful include2,2'-azobis(4-methoxyl-2,4-dimethylvaleronitrile), dimethyl2,2'-azobis-isobutyrate, and the like. Mixtures of two or more of theforegoing azo compounds can be used.

The coating compositions typically contain from about 0.1 to about 10parts by weight of the azo initiator per 100 parts by weight of themultifunctional (meth)acrylate monomer or oligomer, and in oneembodiment about 0.1 to about 5 parts by weight of the azo initiator per100 parts by weight of the multifunctional (meth)acrylate monomer oroligomer, and in one embodiment about 0.1 to about 2 parts by weight ofthe azo initiator per 100 parts by weight of the multifunctional(meth)acrylate monomer or oligomer.

The inventive coating compositions contain dissolved oxygen gastypically at concentrations of about 0.00001 to about 0.5% by weightbased on the total weight of the coating composition, and in oneembodiment about 0.0001 to about 0.5% by weight, and in one embodimentabout 0.0005 to about 0.1% by weight, and in one embodiment about 0.001to about 0.05% by weight. In one embodiment, the oxygen that iscontained in the inventive coating composition is contaminateatmospheric oxygen. An advantage of the present invention is that highgrade coatings can be prepared with the inventive coating compositionseven when contaminate atmospheric oxygen is present in such coatingcompositions.

In one embodiment, the inventive coating composition is a one-packagecoating composition. The term "one-package" is used herein to refer to acoating composition wherein all of the ingredients of the coatingcomposition are combined in one storage stable mixture. Upon applicationthe (meth)acrylate monomer or oligomer is cured under thermal cureconditions. This is distinguishable from a "two-package" system whereinthe ingredients are present in two separate packages and combined at thetime of application or up to about 8 hours prior to the time ofapplication.

In one embodiment, the inventive coating compositions are characterizedby a VOC content of less than about 1 pound of VOC per gallon of coatingcomposition, and in one embodiment less than about 0.7 pound of VOC pergallon, and in one embodiment less than about 0.5 pound of VOC pergallon, and in one embodiment less than about 0.3 pound of VOC pergallon, and in one embodiment less than about 0.2 pound of VOC pergallon, and in one embodiment less than about 0.1 5 pound of VOC pergallon and in one embodiment less than about 0.1 pound of VOC pergallon, and in one embodiment less than about 0.05 pound per gallon, andin one embodiment less than about 0.01 pound per gallon, and in oneembodiment less than about 0.001 pound per gallon. In one embodiment,the inventive coating composition is characterized by the absence of anyVOC. The term "VOC" means volatile organic compound. "Volatile organiccompounds" are defined by the U.S. Environmental Protection Agency (EPA)as organic compounds which participate in atmospheric photochemicalreactions, except for specific designated compounds. The compoundsidentified by the EPA as VOCs are described at 40 CFR 51.100, which isincorporated herein by reference for its disclosure of VOCs.

Depending upon the field of application, the inventive coatingcompositions may also contain a variety of other additives common to thepaint industry such as solvents, pigments, light stabilizers, rheologyagents (e.g., thixotropic agents), mar or slip additives, adhesionpromoters, wetting or dispersing agents, flow control agents, driers,monofuctional (meth)acrylate monomers or oligomers, and mixtures of twoor more of the foregoing.

The solvents that can be used include water, glycol ethers, ketones(e.g., acetone), acetates (e.g., methyl acetate), aliphatic or aromatichydrocarbons, halogenated hydrocarbons, alcohols, and the like. Thesolvents are preferably VOC exempt solvents. The solvent content of theinventive coating composition can range up to about 1 5% by weight, andin one embodiment up to about 5% by weight. An example of a commerciallyavailable VOC exempt solvent that is useful is supplied by OccidentalPetroleum under the trade designation Oxsol 100 which is identified asparachlorobenzotrifluoride.

In one embodiment, the inventive coating compositions are solventless,that is, they contain no solvent.

The pigments that are useful can be inorganic or organic. These includetitanium dioxide, carbon black, phthalocyanine blue or green, ironoxides, quinacridone red, and the like. The concentration of pigment inthe inventive coating composition can range up to about 75% by weight,and in one embodiment about 1% to about 65% by weight, and in oneembodiment from about 5% to about 60% by weight, and in one embodimentabout 10% to about 45% by weight. Examples of commercially availablepigments that can be used include TiONA RCL-535 (a product of Milleniumidentified as titanium dioxide), Hostaperm E3B (a product of Clariantidentified as quinacridone red), and Monarch 1300 (a product of Cabotidentified as carbon black).

The light stabilizers that are useful include hindered amines, arylsalicylates, benzophenones, benzotriazoles, triazines, salacylicacidesters, oxalanilides, formamidines, cyano-acrylates, benzyldenmalonates,and the like. The concentration of light stabilizer in the inventivecoating composition can range up to about 10% by weight, and in oneembodiment from about 0.1% to about 10% by weight, and in one embodimentabout 0.1% to about 5% by weight, and in one embodiment about 0.5% toabout 2% by weight. Examples of commercially available light stabilizersthat can be used include those available from Ciba-Geigy under the tradedesignation Tinuvin. These include Tinuvin 1 23(bis-(1-octyloxy-2,2,6,6,tetramethyl-4-piperidinyl) sebacate) andTinuvin 292 (bis (1,2,2,6,6-pentamethyl-4-piperidinl)sebacate).

The rheology agents that are useful include organo clays, hydrogentatedcaster oils, overbased sulfonate gels, silica gels, and the like. Theconcentration of rheology agent in the inventive coating composition canrange up to about 10% by weight, and in one embodiment from about 0.1%to about 10% by weight, and in one embodiment about 0.1% to about 5% byweight, and in one embodiment about 0.5% to about 3% by weight. Examplesof commercially available rheology agents that can be used includeIrcogel 905 (a product of Lubrizol identified as a gelled sulfonate),Bentone SD-2 (a product of Rheox Inc. identified as a treated clay), andAerosil R972 (a product of Degussa Corp. identified as fumed silica).

The mar or slip additives that are useful include dispersed andmicronized waxes, silicones, polyesters, fluoro surfactants, and thelike. The concentration of mar or slip additive in the inventive coatingcomposition can range up to about 5% by weight, and in one embodimentfrom about 0.05% to about 5% by weight, and in one embodiment about0.05% to about 3% by weight, and in one embodiment about 0.1% to about2% by weight. Examples of commercially available mar or slip additivesthat can be used include Lanco Wax 1780 (a product of Lubrizolidentified as a polytetrafluoroethylene/polyethylene wax), BYK 307 (aproduct of BYK Chemie identified as an organically modifiedpolysiloxane), and EFKA 3232 (a product of EFKA Chemicals identified asan organically modified polysiloxane).

The adhesion promoters that are useful include phosphate esters,silanes, acrylic acid, methacrylic acid, metal salts of acrylic ormethacrylic acid (e.g., zinc diacrylate), vinyl phosphonic acid, vinylsulfonic acid, 2-acrylamido-2-methyl propane sulfonic acid (AMPS),carboxlic acid functional (meth)acrylates, (meth)acrylate functionalurethane monomers and oligomers, and the like. The concentration ofadhesion promoter in the inventive coating composition can range up toabout 10% by weight, and in one embodiment about 0.01% to about 10% byweight, and in one embodiment from about 0.01% to about 5% by weight,and in one embodiment about 0.05% to about 3% by weight, and in oneembodiment about 0.1% to about 2% by weight. Examples of commerciallyavailable adhesion promoters that can be used include Lubrizol 2062 (aproduct of Lubrizol identified as a phosphate ester) and SilquestSilanes (a product of Osi Specialties identified as a silane).

The wetting or dispersing agents that are useful include fatty acidsalts, multifunctional urethanes, polyalkyl ethers, and the like. Theconcentration of wetting or dispersing agent in the inventive coatingcomposition can range up to about 90% by weight based on the weight ofthe pigment, if any, in the coating composition, and in one embodimentfrom about 0.5% to about 90% by weight, and in one embodiment about 0.5%to about 30% by weight, and in one embodiment about 1% to about 15% byweight. Examples of commercially available wetting or dispersing agentsthat can be used include those available from BYK Chemie under the tradedesignation Disperbyk. These include Disperbyk-110 (solution of acopolymer with acidic groups); Disperbyk-111 (copolymer with acidicgroups); Disperbyk-115 (solution of a high molecular weight blockcopolymer with pigment affinic groups); Disperbyk-130 (solution ofpolyamine amides of unsaturated polycarboxylic acids); and BYK-220S(solution of a lower molecular weight unsaturate acidic polycarboxylicacid polyester with a polysiloxane copolymer). Also included are theDisperbyk-116, Disperbyk-160, Disperbyk-161, Disperbyk-162,Disperbyk-163, Disperbyk-164, Disperbyk-166 and Disperbyk-170.

The flow control agents that are useful include acrylic resins,silicones, fluorcarbons, and the like. The concentration of flow controlagent in the inventive coating composition can range up to about 5% byweight, and in one embodiment from about 0.01% to about 5% by weight,and in one embodiment about 0.01% to about 3% by weight, and in oneembodiment about 0.05% to about 1% by weight. Examples of commerciallyavailable flow control agents that can be used include BYK 300 (aproduct of BYK Chemie identified as a polysiloxane), EFKA 3277 (aproduct of EFKA Chemicals identfied as a fluorocarbon modified polymer),Lanco Flow U (a produt of Lubrizol identified as an acrylic polymer, andFluorad FC 431, FC 143 and FC 26 (products of Minnesota Mining andManufacturing Company (3M) identified as fluorocarbons).

The driers that are useful include any of the metallic compositionsnormally used for drying oil, paint, varnish, and the like. These aresometimes referred to as siccatives. The metal compositions that areuseful include the carboxylates of Co, Zr, La, Mn, Ca, Zn, Fe, Al andSn. These compositions are commercially available in the form ofsolutions (in solvents or in excess acid), solventless liquids or solids(powder or postille form). A commercially available drier that can beused is Polcure 503, which is a product of OMG identified as a metalcarboxylate. These driers can be used in the inventive coatingcompositions at concentrations of up to about 2% by weight, and in oneembodiment about 0.01 to about 0.5% by weight.

The monofuctional (meth)acrylate monomers or oligomers can be used at aconcentration of up to about 20% by weight, and in one embodiment about0.1% to about 20% by weight.

The viscosity of the inventive coating composition can be any viscositythat is suitable for applying the coating composition to a substrateusing known application techniques. In one embodiment, the viscosity at20° C. is in the range of about 10 to about 2000 centipoise, and in oneembodiment about 10 to about 1000 centipoise, and in one embodimentabout 10 to about 500 centipoise, and in one embodiment about 40 toabout 350 centipoise.

The inventive coating compositions can be applied as coatings to asubstrate by any of the conventional coating techniques such asbrushing, spraying, dipping, roll coating or flowing. Spray applicationsare particularly advantageous. Any of the known spray techniques may beemployed such as compressed air spraying, airless spraying,electrostatic spraying and either manual or automatic methods.

After application of the inventive coating composition to the substrate,the coated substrate is heated to cure the coating. In the curingoperation, solvents (if present) are driven off and the multifunctional(meth)acrylates are cross linked. Cross linking is initiated by the azoinitiator. An advantage of this invention is that the applying andheating or curing steps are conducted in the presence of oxygen (e.g.,oxygen containing gases such as air). The heating or curing operation isusually carried out at a temperature of at least about 150° F. (65.6°C.). In one embodiment, the heating or curing operation is carried outat a temperature of about 275° F. (135° C.) to about 350° F. (177° C.)for about 10 to about 30 minutes. In one embodiment, it is carried outat a temperature of about 400° F. (204° C.) to about 500° F. (260° C.)for about 45 seconds to about 2 minutes. The coatings as applied are inthe form of thin films. The heating can be effected using anyconventional cure oven. Alternatively, heating can be effected usinginfrared, microwave or radio frequency radiation. The dry film thicknessof the inventive coatings is typically about 0.01 to about 5 mils, andin one embodiment about 0.1 to about 2.5 mils. Any substrate suitablefor coating with a coating composition can be coated using the inventivecoating process. The substrate can be made of metal, wood, plastic, andthe like. These substrates include metal cans, metal sheet, metal plate,metal parts, automotive bodies, automotive body parts, and the like.

EXAMPLES

The coatings exemplified below are subjected to a number of testprocedures. These are as follows.

Brookfield Viscosity:

The Brookfield viscosity in centipoise (cps) is measured with aBrookfield Viscometer Model LVF with Spindle 2 at 60 revolutions perminute at the indicated temperature.

Gloss:

The gloss of the cured coatings is determined at two angles of incidenceof light, namely 60° and 20°, as provided for in ASTM D523-80.

Distinctness of Image (DOI):

The DOI is a measure of the quality of a reflected image on a surface.The DOI of the cured coatings is measured by visual comparison of knownstandards to experimental coatings.

Pencil Hardness:

Pencil leads of increasing hardness values are forced against the filmcoating surface in a defined manner as described in ASTM-D-3363 untilone pencil lead cuts the surface of the film coating. The surfacehardness is considered as the hardest pencil grade which failed to cutthe film coating surface. The pencil leads in order of softest tohardest are as follows: 6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H,6H, 7H, 8H, and 9H.

Non-Volatile Content:

Non-volatile content is a measure of the weight of a coating materialnot evaporated under specified heating conditions. It is determinedusing the procedure described in ASTM D 3960.

MEK Double Rubs:

MEK (methyl ethyl ketone) double rubs are used to measure the extent towhich a coating has cured. The procedure involves rubbing the surface ofa coating using an MEK saturated cotton cloth with a back and forthmotion over a test area of two inches for the indicated number of rubs.

Radius Bend:

Radius bend is a measure of film flexibility. The procedure is describedin ASTM D 4145.

Cross hatch adhesion is a measure of the adhesion of a film to asubstrate. The procedure is described in ASTM D3359.

Reverse Impact:

Reverse impact is used to measure film flexibility and adhesion. Theprocedure involves dropping a one-pound conical weight on the reverseside of a coated metal panel from a given height measured in inches.Reverse impact values are reported in inch-pounds.

Example 1

Part A

The following materials are mixed with stirring at 40° C. for 24 hoursto form an acrylate functional urethane prepolymer:

    ______________________________________                                                       Wt. (grams)                                                    ______________________________________                                               SR 495  122.270                                                          Desmodur I 39.506                                                             Dabco T-12 0.016                                                            ______________________________________                                    

SR 495 is a product of Sartomer Company identified as caprolactoneacrylate. Desmodur I is a product of Bayer identified as isophoronediisocyanate. Dabco T-12 is a product of Air Products identified as anorgano tin catalyst.

Part B

The following ingredients are mixed at a temperature of 25° C., strippedusing a vacuum (less than or equal to 5 mmHg absolute), and thenfiltered to provide the desired coating composition.

    ______________________________________                                                         Wt. (grams)                                                  ______________________________________                                        Product from Part A                                                                            40.00                                                          SR-492 160.00                                                                 Vazo 88 2.00                                                                  Byk 331 0.40                                                                  Polycure 503 0.04                                                           ______________________________________                                    

The non-volatile content of the resulting coating composition is 98.9%by weight. The viscosity at 22° C. is 193 centipoise. The coatingcomposition is spayed from an HVLP (high volume low pressure) spray gunonto a cured Ford OEM automotive topcoat and cured at 270° F. (132.2°C.) for 30 minutes. The resulting coating has a thickness of 2 mils. Thecoating exhibits a pencil hardness of 3H, high gloss (20° gloss =81.5,60° gloss =88.5), excellent DOI, and excellent flexibility (panel isbent around a 5T (5 times the thickness of the panel) radius at greaterthan 90° without damage to the coating).

Example 2

The following ingredients are blended together at room temperature in astainless steel dispersion cup:

    ______________________________________                                                            Wt. (grams)                                               ______________________________________                                        Caprolated Trimethylolpropane                                                                     30.13                                                       trimethacrylate                                                               Disperbyk 111 4.75                                                            Disperbyk 116 15.77                                                           Hydroquinone 0.0034                                                         ______________________________________                                    

TiONA RCL-535 (157.2 grams) is added to the mixture using a spatula. Themixture is mixed using a high speed disperser (10,000-25,000 rpm) for 13minutes. The temperature of the mixture increases to 40-50° C. Theresulting mixture is a pigment dispersion having a pigment to binderratio of 4:1.

The following ingredients are added to the foregoing pigment dispersionwith stirring:

    ______________________________________                                                      Wt. (grams)                                                     ______________________________________                                               SR-492 68.00                                                             SR-501 67.82                                                                  BYK-307 0.349                                                               ______________________________________                                    

The mixture is stripped under vacuum (less than or equal to 5 mm Hgabsolute) for two hours at a temperature of 40-60° C. while bubbling dryair through the mixture. Vazo 64 (2.00 grams) is added to the mixture atatmospheric pressure. The mixture is stirred for 30 minutes at atemperature of 30-35° C. and then filtered through a 30 micron filter.The resulting coating composition has the following characteristics:

    ______________________________________                                        Pigment to binder ratio:                                                                              0.9:1                                                   Non-volatile Content: 98.3%                                                   Viscosity @ 25° C.: 165 cps                                          ______________________________________                                    

The coating composition is sprayed on to ground and treated Bonderite1000 steel panels. (Bonderite 1000 steel panels are available from QPanel Lab Products. They have a machined surface treated with ironphosphate.) The dry film thickness is 1.5-1.9 mils. The coating issprayed using an HVLP touch-up gun at pressure of 45 psi and baked for15 minutes at 300° F. (149° C.). The coating exhibits good hiding andhas the following characteristics:

    ______________________________________                                        Pencil hardness:        3H                                                      Cross hatch adhesion 5B                                                       100 MEK double rubs: Passed                                                   180° 0.5 inch radius bend: Passed                                      60° Gloss: 118%                                                        DOI: High                                                                   ______________________________________                                    

After one hour exposure to boiling water, the cross-hatch adhesionrecovery is 4B after 5 minutes, and 5B after 30 minutes.

Example 3

Part A

The following ingredients are added to a 500 ml flask equipped with adry air inlet and a magnetic stir bar. The mixture is stirred at roomtemperature with dry air bubbling through the mixture for 30 minutes,heated to 60° C. over a period of 30 minutes and held at 60° C. for anadditional 60 minutes to provide the desired product.

    ______________________________________                                                       Wt. (grams)                                                    ______________________________________                                               SR 495  303.36                                                           Desmodur I 100.00                                                             Dabco T-12 0.0330                                                           ______________________________________                                    

Part B

The following ingredients are mixed at a temperature of 25° C., strippedusing a vacuum (less than or equal to 5 mmHg absolute), and thenfiltered to provide the desired coating composition.

    ______________________________________                                                          Wt. (grams)                                                 ______________________________________                                        Product from Part A                                                                             28.48                                                         SR 492 113.93                                                                 SR 501 34.56                                                                  Vazo 64 2.21                                                                  BYK 331 0.346                                                                 Vinylphosphonic acid 0.182                                                  ______________________________________                                    

The coating composition has the following properties:

    ______________________________________                                        Non-Volatile Content:  99.2%                                                    Viscosity @ 24° C.: 145 cps                                          ______________________________________                                    

Part of the coating composition is sprayed on to bare steel panels at adry film thickness of 1.0-1.2 mils using an HVLP touch-up gun at apressure of 45 psi and baked for 20 minutes at 300° F. (149° C.). Thecoating has the following characteristics:

    ______________________________________                                        Pencil hardness:          3H                                                    Cross hatch adhesion (ASTM D3359): 5B                                         100 MEK double rubs: Passed                                                   180° 3T radius bend (three times Passed                                the thickness of the substrate):                                              DOI: High                                                                   ______________________________________                                    

After one hour exposure to boiling water, the cross-hatch adhesionrecovery is 5B after 5 minutes, and 5B after 30 minutes.

The remaining part of the coating composition is sprayed on to barealuminum panels at a dry film thickness of 0.4-0.7 mil using an HVLPtouch-up gun at pressure of 45 psi and baked for 20 minutes at 300° F.(149° C.). The coating has the following characteristics:

    ______________________________________                                        Pencil hardness:        3H                                                      Cross hatch adhesion: 5B                                                      100 MEK double rubs: Passed                                                   180° 0.25 inch radius bend: Passed                                     DOI: High                                                                   ______________________________________                                    

After one hour exposure to boiling water, the cross-hatch adhesionrecovery is 5B after 5 minutes, and 5B after 30 minutes.

Example 4

The following ingredients are mixed at atmospheric pressure and atemperature of 25° C., stripped a under vacuum (less than or equal 5mmHg absolute), and then filtered to provide the desired coatingcomposition.

    ______________________________________                                                          Wt. (grams)                                                 ______________________________________                                        SR 492            5.538                                                         SR 501 10.42                                                                  Vazo 64 0.1529                                                                BYK 307 0.0184                                                                Acrylic acid 0.1644                                                           Vinylphosphonic acid 0.0274                                                 ______________________________________                                    

The coating composition has the following properties:

    ______________________________________                                        Non-Volatile Content:  99.0%                                                    Viscosity @ 24° C.: 90 cps                                           ______________________________________                                    

The coating composition is sprayed on to bare steel panels at a dry filmthickness of 0.9-1.1 mils using an HVLP touch-up gun at a pressure of 45psi and baked for 20 minutes at 300° F. (149° C.). The coating has thefollowing characteristics:

    ______________________________________                                        Pencil hardness:         3H                                                     Cross hatch adhesion: 5B                                                      100 MEK double rubs: Passed                                                   180° 0.25 inch radius bend: Passed                                     DOI: High                                                                   ______________________________________                                    

Example 5

The following ingredients are added to a 0.5 pint stainless steel beakerand ground to a Hegman of 7.5 using a Premier Mill with Cowles blade at3000 rpm for 10 minutes:

    ______________________________________                                                            Wt. (grams)                                               ______________________________________                                        Caprolated trimethylolpropane                                                                     30.13                                                       trimethacrylate                                                               Disperbyk 111 4.75                                                            Disperbyk 161 15.77                                                           Hydroquinone 0.034                                                            TiONA RCL-535 157.20                                                        ______________________________________                                    

The foregoing composition is the letdown into a premix of the followingingredients in a pint paint can, and the total mix stirred at 500 rpmfor 10 min.:

    ______________________________________                                                      Wt. (grams)                                                     ______________________________________                                               SR-492 68.00                                                             SR-501 67.82                                                                  Byk 307 0.349                                                                 VAZO 67 2.00                                                                ______________________________________                                    

Without further workup, the resulting coating has the followingcharacteristics:

    ______________________________________                                        Pigment to binder ratio:  0.9:1                                                 Non-volatile content: 96.4%                                                   Viscosity @ 25° C. (Brookfield, 20 rpm) 180 cps.                     ______________________________________                                    

The coating is drawn on a Bonderite 1 000 panel using a No. 20 wirewound drawdown bar, and baked for 15 minutes at 150° C. The dry filmthickness is 1.2-1.3 mils and the film has the followingcharacteristics:

    ______________________________________                                        Pencil Hardness      2H                                                         Cross Hatch Adhesion 5B                                                       Reverse Impact 60 inch pounds                                                 60 Degree Gloss 93                                                          ______________________________________                                    

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

I claim:
 1. A process for coating a substrate comprising the stepsof:applying a thin film of a coating composition to said substrate; saidcoating composition comprising a monomer or oligomer containing two ormore acrylate and/or methacrylate functional groups, an azo initiatorand oxygen, said coating composition having a VOC content of less thanabout one pound of VOC per gallon of said coating composition; andheating said coating composition at an effective temperature for aneffective period of time to cure said coating composition, said applyingand heating steps being conducted in the presence of oxygen.
 2. Theprocess of claim 1 wherein said composition has a VOC content of lessthan about 0.7 pound of VOC per gallon of said composition.
 3. Theprocess of claim 1 wherein said composition is a one-package coatingcomposition.
 4. The process of claim 1 wherein said composition has aviscosity at 20° C. in the range of about 10 to about 2000 centipoise.5. The process of claim 1 wherein said monomer or oligomer furthercomprises at least one functional group attached to it, said functionalgroup being selected from the group consisting of epoxy, hydroxy,carboxy, sulfonic, phosphonic, isocyanate, vinyl, allyl, halide, amine,sulfonamide, carbamide, carbodiimide, cyano, acetylenic, aldehyde,peroxy, hydroperoxy, azo, peroxyester, and combinations of two or moreof the foregoing.
 6. The process of claim 1 wherein said monomer oroligomer is a compound represented by the formula ##STR6## wherein informula (I): R is a hydrocarbon group, a siloxane group, a partiallyfluorinated hydrocarbon group or a perfluorocarbon group;each A isindependently a divalent group derived from an epoxide, a mixture ofdiol and dicarboxylic acid, a lactone, a lactam, an amino acid, ahydroxy acid or lactide; each B is independently hydrogen, a hydrocarbongroup, a perfluorinated hydrocarbon group, or a group represented by theformula ##STR7## wherein in formula (II) R¹ is hydrogen, a hydrocarbongroup, a siloxane group, a partially fluorinated hydrocarbon group or aperfluorocarbon group; x is a number in the range from zero to about 50;and y is a number in the range from 2 to about
 10. 7. The process ofclaim 1 wherein said monomer or oligomer is a compound selected from thegroup consisting of triethylene glycol dimethacrylate, ethylene glycoldimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycoldimethacrylate, 1,3-butylene glycol diacrylate, 1,4-butanedioldiacrylate, 1,4-butanediol dimethacrylate, diethylene glycol diacrylate,diethylene glycol dimethacrylate, 1,6-hexanediol diacrylate,1,6-hexanediol dimethacrylate, neopentyl glycol diacrylate, neopentylglycol dimethacrylate, polyethylene glycol dimethacrylate, tetraethyleneglycol diacrylate, triethylene glycol diacrylate, 1,3-butylene glycoldimethacrylate, tripropylene glycol diacrylate, polyethylene glycoldiacrylate, cyclohexane dimethanol dimethacrylate, cyclohexanedimethanol diacrylate, ethoxylated bisphenol A diacrylate, ethoxylatedbisphenol A dimethacrylate, propoxylated neopentyl glycol diacrylate,alkoxylated aliphatic diacrylate, trimethylolpropane trimethacrylate,trimethylolpropane triacylate, tris (2-hydroxy ethyl) isocyanuratetriacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritoltriacrylate, propoxylated trimethylolpropane triacrylate, propoxylatedglyceryl triacrylate, pentaerythritol tetraacrylate,di-trimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate,ethoxylated pentaerythritol tetraacrylate, pentaacrylate ester, andmixtures of two or more thereof.
 8. The process of claim 1 wherein saidmonomer or oligomer is a propoxylated trimethylolpropanetri(meth)acrylate.
 9. The process of claim 1 wherein said monomer oroligomer is a urethane containing multifunctional (meth) acrylatemonomer or oligomer.
 10. The process of claim 1 wherein said monomer oroligomer has a molecular weight in the range of about 200 to about 5000.11. The process of claim 1 wherein said azo initiator is a compoundselected from the group consisting of2,2'-azobis(2,4-dimethylpentanenitrile),2,2'-azobis(2-methylpropanenitrile), 2-2'-azobis(2-methylbutanenitrile),1,1'-azobis(cyclohexanecarbonitrile),2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile),dimethyl-2,2'-azobis-isobutyrate, and mixture of two or more thereof.12. The process of claim 1 wherein said monomer or oligomer is presentin said composition at a concentration in the range of about 5% to about99.9% by weight.
 13. The composition of claim 1 wherein said compositioncomprises is about 0.1 to about 10 parts by weight of azo initiator per100 parts by weight of said monomer or oligomer.
 14. The process ofclaim 1 wherein said composition further comprises a solvent, pigment,light stabilizer, rheology agent, mar or slip additive, adhesionpromoter, wetting or dispersing agent, flow control agent, drier,monofunctional (meth)acrylate monomer or oligomer, or a mixture of twoor more thereof.
 15. The composition of claim 1 wherein said compositionis solvent free.
 16. The process of claim 1 wherein said applying stepcomprises spraying said coating composition.
 17. The process of claim 1wherein said substrate is a metal can, metal sheet, metal plate, metalpart, automotive body or automotive body part.
 18. The process of claim1 wherein said heating step is conducted at a temperature of at leastabout 150° F. (65° C.).
 19. The process of claim 1 wherein said applyingand heating steps are conducted in the presence of air.
 20. The processof claim 1 wherein said heating is effected using infrared, microwave orradio frequency radiation.